In a cellular radio system, the served area is divided into cells. Each cell is served by one base station. An active mobile station in a cell remains in radio contact with the serving base station. In normal operation, when a mobile engaged in active conversation moves from one cell to another, the cellular system will perform a hand-off in which the mobile station is instructed to tune to a new channel served by the base station of the cell it is entering.
In order to provide more efficient hand-offs and traffic management, a cellular system needs to know the approximate location of all the mobile stations engaged in active calls. In addition, a cellular system may also provide a mobile station location service. This service can provide information on the location of mobile station to the authorized service subscriber, even if the mobile is not engaged in an active call.